How can I check if the information on the slave is equal to the
information on the master. I try running ldapsearch on the slave looking
for user thats only on the master but even after the replication starts
the user is not on the slave. Do I need to copy the whole data from the
master first so they are in sync before I start the replication, or the
slave will get the missing info from the master?

Make sure there is no ACL on the master that prevents the slave from
reading some information. I noticed it quickly breaks the sync.